P: Slideshow video exportation: does not take edits into account

Version 9.3, an update to Lightroom Classic, went live on June 15, 2020 and contains a fix for this issue. Please install the update and respond back if it does not cure the issue for you. Thank you for your patience!

Thanks Rikk!

Ok. I've duplicated what you are seeing and logged a bug. Thanks for the report and the instructions. 

Yes.

But if you DON’T scroll through the grid view and don’t update the previews and generate the video, LR uses the « previous » previews instead of the right ones.

Ok. I was able to reproduce with these steps. 

If I go to Grid before Slideshow and scroll through all the images until I see the visual update of the file, it appears to generate correctly. Does that match your experience?

Right 😉

Revision:

Create Collection of 485 Images all in color
Select one image
Convert to Black and White
Sync to other 484 images
Go to Slideshow and Export collection as video

Is that right?

No, I'm talking about LR Classic only, so no cloud sync involved.
I'm talking about edit sync in the develop module:

This is the test I ran:

Create Collection of 485 Images all in color and synced
Convert all Images to Black and White
Allow edits to sync to cloud
Go to Slideshow and Export collection as video

Do I have that correct or did I miss something?

A typical scenario:
Syncing all the images with the desired edits, wait until synced (of course) and then try to export through the Slideshow module.

A more advanced workflow involves "reading metadata from file" instead of syncing edits from one picture, but the end result is the same.

For what I understood, LR seems to render correctly only the images that have been rendered (not per se 1:1 previews) in the Library view. I mean, when you sync edits, and view an image, it takes some time (sometimes a fraction of second) to display the synced edits. If there are a lot of images, a lot of them are not displayed and thus not rendered.
Rendering the 1:1 preview is just a (long) workaround to force rendering. This is, however, overkill for the 1080p limit of LR.